I. Field of the Invention
The present invention relates generally to checkweigher and grading systems, and more particularly to a modular checkweigher and grading system wherein the weighing platform includes the conveyor assembly, including air powered motors for driving the conveyor belts.
II. Description of the Prior Art
Checkweigher/grader systems are commonly known in the art. These systems are generally used to check the weight of objects moving across a high-speed conveyor, and to determine if the weight of the object is within a desired range.
In the majority of prior-art checkweigh systems, a weighing platform connected to a load cell is centrally located under a slackened belt or chain which carries the item to be weighed. The belt or chain is sufficiently slack to allow the item to momentarily come to rest on the weighing platform. Such a system is shown for example in Del Resso, U.S. Pat. No. 3,180,475. These systems often produce errors in the weight reading caused by the slackening of the belt. In order to overcome the problem of belt slackening, prior patents have either attempted to electronically filter the oscillation errors, or employed mechanical assemblies to reduce the error.
De Santo, U.S. Pat. No. 4,023,668 discloses a conveyor in which the entire conveyor belt, and drive means are located on top of the load cell. This system reduces the error due to slackening, but because a portion of the belt remains supported only by end pulleys, slackening errors still result.
Other examples of systems to reduce checkweigher error include, for example, Hall, Jr. et al, U.S. Pat. No. 4,231,439, and Yano, U.S. Pat. No. 3,714,401.
An additional problem with prior art checkweigh systems is that they were not suitable for harsh environments, such as processing chickens. These mechanical systems are difficult to repair and clean, and often breakdown in the harsh environment. In the event of a breakdown, the entire line must be stooped until a repair is effectuated. Further, the mechanical apparatus used in these systems, especially the electrical motors and chain drives, require extensive, and expensive maintenance procedures.
Grading systems are also commonly known. Most of these systems likewise require much maintenance to operate in harsh environments. For example, most conveyors are extremely difficult to clean or dry in the event of a spillage. The conveyor belts may difficult to lift, and the control boxes may not be moved for cleaning. If a breakdown occurs, the entire line may remain idle until repaired.
None of the prior art systems provide a checkweigher/grader system in which the conveyors may be easily removed, replaced or cleaned; in which the conveyor belt remains in contact with both the upper and lower surfaces of the weighing platform for reduced slackening errors; in which the weight of the drive mechanism is included as part of the weight applied to the load cell, including low maintenance motors; and in which modular, reconfigurable, easily cleanable grader units are used.